BACKGROUND
The prevalence of childhood obesity has increased dramatically and it has been hypothesized that early environmental influences may contribute to the development of obesity. For instance, maternal smoking during pregnancy has been associated with obesity. Recent reviews support the hypothesis that early exposure to environmental endocrine-disrupting chemicals may increase body weight. These chemicals include the pesticides dichlorodiphenyldichloroethylene (DDE) and hexachlorobenzene, dioxin-like compounds, and polychlorinated biphenyls (PCBs). DDE is the main metabolite of the pesticide DDT (dichlorodiphenyltrichloroethane). DDE, hexachlorobenzene, PCBs, and dioxins are all considered endocrine disruptors, defined as chemical substances that mimic or affect levels of endocrine mediators.

Few prospective studies have investigated the association between prenatal exposure to chemicals and body mass index (BMI). In this study the authors investigated the association between BMI during the first 3 years of life and prenatal exposure to environmental pollutants hexachlorobenzene, DDE, dioxin-like compounds, and PCBs.

METHODS
The participants were drawn from a large biomonitoring study, which included a total of 1,196 mothers and their newborns enrolled from 26 maternity wards in Flanders, the northern part of Belgium, between September 2002 and February 2004. The maternity wards were selected through stratified sampling. An average of four wards were selected from each of the following strata: two urban areas, an area characterized by fruit orchards, a rural area, and four industrial areas. Fifty participants were recruited from each maternity ward.

The present data are from a longitudinal substudy of a random sample of mother-infant pairs (n=138) living in the urban area of Antwerp or in rural Flanders with follow-up until the children were 3 years of age. Initial questionnaires collected information on the parents, including health status, smoking behavior, age, family composition, socioeconomic status, and the height and weight of the parents. The authors sent postal questionnaires every 6 months for children between the ages of 3 weeks and 36 months, collecting information about the child’s demography, diet, and health status and whether the child was breast-fed. Household income was used as an indicator of socioeconomic status.

Data on height and weight of the children was collected by questionnaires administered at birth and at 12, 18, 24, 30, and 36 months of age. Parents filled in the height and weight measurements for their children obtained during physician visits or with Child and Family Services. BMI (kilograms per square meter) was determined from questionnaire responses and converted to BMI standard deviation scores [BMI SDS = (child’s BMI – population mean BMI)/population standard deviation], using Flemish growth curves.

The researchers collected 30 mL of cord blood from each participating birth mother. Two laboratories measured levels of PCBs and chlorinated pesticides the cord blood by gas chromatography.

At 1 year of age, children of smoking mothers had a higher BMI SDS compared with children of nonsmoking mothers.

Among children of non-smoking mothers, the effect of increasing DDE levels on BMI SDS at 3 years of age was small (the difference in BMI SDS for a DDE level of 450 ng/g and a DDE level of 63.7 ng/g = 0.13).

Smoking enhanced the relation between DDE and BMI SDS at 3 years (difference in BMI SDS for DDE concentrations between the 90th and 10th percentiles = 0.76)

No association was found between BMI SDS and hexachlorobenzene and dioxin-like compounds.

DISCUSSION
The findings of this study demonstrate that intrauterine exposure to DDE and PCBs is associated with BMI during early childhood. Specifically, DDE had a small association with BMI SDS in 3-year-old children of nonsmoking mothers. However, this association was enhanced in children of smoking mothers. PCBs were also associated with higher BMI SDS values.

The results should be considered in light of several important limitations. For instance, this study related reported results to BMI SDS until a child reached 3 years of age. Although there is a correlation between BMI during preschool age and adult BMI, the authors acknowledge that they do not know whether the correlation with BMI will persist into later periods and whether these children will actually become overweight or obese. There are also significant regional differences in exposure to these pollutants in the Flanders area, so the findings cannot be generalized to the entire population of Flanders.

BOTTOM LINE
This study documents that intrauterine exposure to DDE and PCBs is associated with increased BMI during early childhood. The association with PCBs starts from birth, with a negative effect on birth weight and birth length, whereas the association with DDE is measurable between 1 and 3 years of age, with no effect on birth weight or length.